<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<input type="text">
<input type="button" value="平方" onclick="f()">
<input type="button" value="求和" onclick="f1()">
<div>结果:</div>

<script>
    let d = document.querySelector("div");
    let i = document.querySelector("input");
    function f(){
        if (isNaN(i.value)){
            d.innerText = "输入错误!";
            return;
        }
        d.innerText = "结果=" + i.value*i.value;
    }
    function f1(){
        // d.innerText = "结果=" + (i.value/1 + i.value/1);
        d.innerText = "结果=" + (parseFloat(i.value)+parseFloat(i.value));
    }

</script>



</body>
</html>